Lithium titanium bismuth cobalt ferrites

ABSTRACT

MICROWAVE FERRITES WITH HIGH POWER HANDLING CAPABILITY, NARROW RESONANCE LINEWIDTHS, GOOD TEMPERATURE PERFORMANCE, LOW LOSSES, LOW COSTS, AND RECTANGULAR HYSTERESIS LOOPS ARE MADE FROM A LITHIUM-TITANIUM-BISMUTH FERRITE CONTAINING A SMALL AMOUNT OF COBALT. IN ADDITION, SMALL AMOUNTS OF ZINC OR MANGANESE CAN BE PRESENT IN THE FERRITES.

Sept. 26, ET AL LITHIUM TITANIUM BISMUTH COBALT FERRITES Filed Sept. 7, 1971 gg: masmw 0 0 2 E E g Amaum of coba/f in lifhium fifonium bismufh ferr/fe JAN SM/T A m A B A A B n L MM V n A DM L Mm M Pu INVENTORS (m/W g [@y ATTOKNEV United States Patent 01 fice US. Cl. 25262.59 3 Claims ABSTRACT OF THE DISCLOSURE Microwave ferrites with high power handling capability, narrow resonance linewidths, good temperature performance, low losses, low costs, and rectangular hysteresis loops are made from a lithium-titanium-bismuth ferrite containing a small amount of cobalt. In addition, small amounts of zinc or manganese can be present in the ferrites.

T he invention herein described was made in the course of or under a contract with the Department of the Air Force.

SUMMARY OF THE INVENTION At the present time, garnets are ordinarily employed at microwave frequencies. However, garnets are expensive and have poor temperature performance. Although it has been suggested that ferrites might be used, the losses have been high, the densities have been low or the coercive forces have been too high.

In accordance with the invention of Argentina and B'aba, Ser. No. 863,683, filed Oct. 3, 1969, now Pat. No. 3,630,912, these difficulties are obviated by employing at microwave frequencies, ferrites which have narrow resonance linewidths, good temperature performance, low losses, low costs and rectangular hysteresis loops. This is accomplished by making a ferrite containing lithium and titanium with a small amount of bismuth. Copper, zinc and manganese may also be present. Although this former invention was a distinct advance in the art, it was found that such ferrites were suitable only for low power microwave devices. For power levels above the 1 to 2 kilowatt range, instabilities developed in the ferrite which caused a large power loss.

In accordance with the present invention the power handling capability of such ferrites is greatly enhanced by the addition of a small amount of cobalt.

BRIEF DESCRIPTION OF THE DRAWING The sole figure of the drawing is a graph showing the effect on power handling capability of ferrites containing varying amounts of cobalt.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following preparative procedure is used in compounding ferrite materials in accordance with the present invention:

Oxides of the constituent metal ions are generally employed when possible. In instances where the chemical instability of the oxide of a particular metal ion causes said oxide to be an impure and unreliable compound, the anhydrous carbonate of the metal ion is used. The raw materials are weighed out in stoichiometric proportions and are wet mixed for one hour or more in a ball mill. The resulting slurry is then dried at around 100 C. and the dried raw material mixture is then forced through a standard 20 mesh screen for ease of handling.

The screened oxide mixture is then loaded into refractory boats. The boats are placed in a box type furnace, and

Patented Sept. 26, 1972 heated to a predetermined temperature. The exact temperature can vary from 700 C. to 900 C. The object of this step is twofold: the primary object is to provide sufiicient energy to react the oxide mixture to a 70% ferrite 30% oxide mixture by a solid state reaction. The secondary objective is the simple thermal decomposition of any carbonates used.

The reacted mixture is generally characterized by a relatively large predominant particle size. Before the mixture can be shaped and sintered into a single phase ferrite body the particle size must be reduced. Ball milling is employed in essentially the same manner as outlined above. The ferrite-oxide slurry is then dried at around C. to a fine powder.

The powder is then mixed with a binder as is well known to those skilled in the art. Wide latitude is permissible in the selection of binders. A typical binder is polyvinyl alcohol.

The addition of the binder can be carried out in the second ball milling step, or in an additional step employing any sort of method facilitating uniform distribution of the substance used as a binder. The binder impregnated powder is then shaped in tool steel dies with enough pressure to facilitate uniform compaction.

The pressed shapes are then sintered at temperatures ranging from 950 C. to 1150 C. in atmospheres of oxygen or air.

The novel ferrites of the present invention have the following composition:

0.00-1a 0.1 000056550065 030 x 095 0 22 0.20 O W OA, and

The following non-limiting examples illustrate various preferred embodiments of the invention. In the examples, Example 1 illustrates a composition which does not contain cobalt while Example 2 shows the same composition with the addition of cobalt showing the beneficial effect of the cobalt addition:

EXAMPLE 1 A ferrite was prepared by the above procedure. The reaction step was performed at 800 C. The sintering step was performed at 1025 C. in an air atmosphere.

The composition where had the following microwave properties: Dielectric loss tangent-=0.0005, magnetic loss tangent-=0.0005, resonance linewidth=2115 oersteds, spin Wave linewidth=2.5 oersteds, peak power handling capability=1.3 kilowatts.

3 EXAMPLE 2 A composition where 19:0.002 x=0.66 z=0.05 w=0.10 oc=0.006

had the following microwave properties: Dielectric loss tangent=0.0005, magnetic loss tangent=0.0007, resonance linewidth=210 oersteds, spinwave linewidth=6.2 oersteds, peak power handling capability=7.0 kilowatts.

As can be seen, Example 2 wherein cobalt was employed has a factor of greater peak power handling capability than does Example 1 which has no cobalt. Example 2 has a slightly larger magnetic loss tangent than does Example -1; otherwise, the usefulness of Example 2 as a microwave material has not been impaired by the addition of cobalt.

EXAMPLES 3-8 A series of ferrites was prepared of the series wherein w=0.10 and wherein a was varied from 0 to 0.01 in 0.002 increments. The square of the spin Wave linewidth, a property directly proportional to the power handling capability of a'microwave ferrite, was measured and plotted on the figure of the drawing. This was found to increase by a factor of 15 over the range of 04 values tried.

We claim:

1. A lithium-titanium-bismuth cobalt ferrite having the following compositions:

where 0.001 OL 0.1 0000551 50065 0.30sx0.95 0 zs0.20 05w50.4, and

2. A ferrite in accordance with claim 1 wherein a: 0.006.

3. A ferrite in accordance with claim 1 wherein a: 0.002.

References Cited UNITED STATES PATENTS 0 TOBIAS E. LEVOW, Primary Examiner J. COOPER, Assistant Examiner U.S. c1. X.R. 25262.61, 62.62 

